1. Field of the Invention
The invention relates to methods for working a ceramic material and, more particularly, relates to a method in which drilling, cutting, engraving and other working can be applied to a ceramic material used in an electronic substrate material, an electronic device and structural member and the like in an efficient, precise and minute manner.
2. Description of the Background Art
A ceramic material has a superior characteristic in that it has greater strength and hardness compared with general metals. Since the ceramic material shrinks by more than ten percents when formed by baking, a secondary working is essential to obtain parts formed by the ceramic material, having a high accuracy. This secondary working is, however, extremely difficult because of the great strength and hardness of the ceramic material.
Conventionally, grinding and ultrasonic machining and so on have been used in drilling, cutting and engraving of the ceramic material. When the ceramic material is worked with such a mechanical working, however, cracks tend to be caused in the ceramic material. Accordingly, it is difficult to work a ceramic material with high accuracy by such a mechanical working. Furthermore, the abovementioned methods entail a problem that a tool to be used is worn out and the efficiency of working is low.
Japanese Patent Laying-open No. 63-190789 by Ishii discloses a method in which the ceramic material is worked by photoetching. Referring to FIGS. 1A-1C, a method by photoetching will now be described below. In this method, firstly, as shown in FIG. 1A, a heat-and acid-resistant photoresist 2 is applied on the surface of a work piece 1. A desired work pattern is then transcribed on the resist by exposure, and an unnecessary portion is washed and removed to form a resist pattern 3 as shown in FIG. 1B. Subsequently, etching is effected with a phosphoric acid boiling at a high temperature (300.degree. C.) to a desired depth to form grooves 4 as shown in FIG. 1C. After that, the resist is peeled with a remover.
In accordance with the method by photoetching, however, working is effected in a corrosive atmosphere at a high temperature, so that the resist is easily damaged during etching. The damage of the resist makes it easier to cause defects to the work piece. A cost is also increased for protecting the container for effecting etching from corrosion and damages. An operation of etching also involves dangers. Furthermore, there still remain problems as common to a general etching method, that working rate is low, that the efficiency of working is low, and that it is impossible to work until the aspect ratio (the depth of working/the width of working) is 1 or more.
On the other hand, a method of non-contact working with laser has been developed. Japanese Patent Laying-open No. 2-38587 by Morita and et al. discloses a working method using a working by laser and a wet etching. In this method, firstly, a melted-solidified layer is formed on a work piece by irradiation of a laser beam to the work piece. Next, the work piece is wet etched in an etchant having a high etching rate with respect to the melted-solidified layer. The melted-solidified layer is removed by etching.
Japanese Patent Laying-open No. 64-77506 by Takeuchi and et al. also discloses a working method in which laser and etching treatment is used. In this method, firstly, working such as drilling or cutting is applied to a work piece of a ceramic material by irradiation of a laser. The ceramic material is metallized in the worked portion. The metallized portion is then removed by etching.
These methods could only be applied to materials which are melted-solidified or metallized in the portion irradiated by a laser. The materials include metals (especially alloys) capable of being melted-solidified by a laser and a nitride ceramic material (for example, silicon nitride (Si.sub.3 N.sub.4) and aluminum nitride (AlN) and the like) capable of being metallized by a laser, whereas they don't include an oxide ceramic material (for example, alumina) and a carbide ceramic material (for example, silicon carbide (SiC)) for which it is extremely difficult to be metallized. When oxide or carbide ceramic materials were worked by these methods, there was little difference between the portion irradiated by a laser and the portion which was not irradiated with respect to a characteristic resisting the etchant. Accordingly, it was very difficult to selectively apply etching only to the portion which had been irradiated by the laser. Additionally, a minimum size to be worked could not be made smaller than the normal size to be worked by a laser in a method in which etching is effected after the work piece is cut or drilled by a laser.